Method and apparatus for generating an infrared illumination beam with a variable illumination pattern

ABSTRACT

A method for generating an infrared (IR) beam for illuminating a scene to be imaged comprises providing at least two IR emitters, including a first IR emitter operable to emit a wide beam component of the IR beam, and a second IR emitter operable to emit a narrow beam component of the IR beam, wherein the wide beam component has a linear profile that has a lower standard deviation than a linear profile of the narrow beam component. The method also comprises selecting a desired linear profile for the IR beam, and selecting a power ratio of power directed to the first IR emitter and power directed to the second IR emitter that produces the IR beam with the desired linear profile when the narrow beam component and wide beam component are combined; and directing power to the first and second IR emitters at the selected power ratio to generate the wide and narrow beam components, and combining the generated wide and narrow beam components to produce the IR beam.

CROSS REFERENCE TO RELATED APPLICATION

This claims the benefit of U.S. Provisional Application No. ______,filed Jan. 15, 2013, which is incorporated herein in its entirety byreference.

FIELD

This disclosure relates generally to a method for generating an infrared(“IR”) illumination beam with a variable illumination pattern, and an IRilluminator for performing such method. Such IR illuminator can be partof an imaging apparatus having a zoom lens, and generate an IRillumination beam with an illumination pattern that varies with thefocal length of the zoom lens.

BACKGROUND

Some conventional security or surveillance cameras use varifocal lensesthat allow an adjustable field-of-view. When equipped with an IRilluminator, the illumination pattern is fixed for all focal lengths andis generally optimized for a specific field of view at one focal length.For field of views that are larger than the optimized field of view, anon-optimal illumination pattern will appear as a bright spot in thecentre of the image, saturating the sensor in that region and obscuringdetail. Conversely, for field of views that are narrower than theoptimized field of view, some of the illumination power will beprojected outside of the imaging area and therefore be wasted. As aresult, a less than optimal IR image is captured by surveillance camerasthat use such IR illuminators.

SUMMARY

According to one aspect of the invention, there is provided a method forgenerating an infrared (IR) beam for illuminating a scene to be imaged.The method comprises providing at least two IR emitters, including afirst IR emitter operable to emit a wide beam component of the IR beam,and a second IR emitter operable to emit a narrow beam component of theIR beam, wherein the wide beam component has a linear profile with alower standard deviation than a linear profile of the narrow beamcomponent. The method also comprises selecting a desired linear profilefor the IR beam, and selecting a power ratio of power directed to thefirst IR emitter and power directed to the second IR emitter thatproduces the IR beam with the desired linear profile when the narrowbeam component and wide beam component are combined. The method thencomprises producing the IR beam by directing power to the first andsecond IR emitters at the selected power ratio to generate the wide andnarrow beam components and combining the generated wide and narrow beamcomponents. The generated wide and narrow beam components can becombined by directing the centres of the wide and narrow beam componentson the same location in the scene. The desired linear profile of the IRbeam can be defined as having a standard deviation that is less than orequal to a target standard deviation.

The method can further comprise imaging the scene at a selected focallength, wherein the selected focal length has an associated field ofview. The desired linear profile for the selected focal length has astandard deviation that is less than or equal to the target standarddeviation and a highest available irradiance within the field of view.The highest available irradiance can be the power ratio having thehighest proportion of power directed to second IR emitter and whichproduces an IR beam with a standard deviation less than or equal to thetarget standard deviation.

The method can further comprise imaging the scene at different focallengths each having a respective different field of view, and producingan IR beam with a desired linear profile corresponding to each differentfocal length. Each desired linear profile has a standard deviation thatis less than or equal to the target standard deviation and the highestavailable irradiance for the field of view associated with thecorresponding focal length.

The imaging can be performed by an imaging apparatus having a zoom lenswith variable focal lengths, in which case the method comprisesdetermining a current focal length of the zoom lens, selecting thedesired linear profile corresponding to the current focal length,producing an IR beam at the desired focal length, and imaging a sceneilluminated by the IR beam at the current focal length. Selecting thedesired linear profile corresponding to the current focal length cancomprise accessing a beam profile-to-focal length map comprising aseries of focal length increments and their corresponding desired linearprofiles, and selecting the linear profile in the map with acorresponding focal length increment equal to the current focal length.

According to another aspect of the invention, there is provided anapparatus for illuminating a scene to be imaged with infrared radiation,comprising: at least two IR emitters, including a first IR emitteroperable to emit a wide beam component of the IR beam, and a second IRemitter operable to emit a narrow beam component of the IR beam, whereinthe wide beam component has a linear profile that has a lower standarddeviation than a linear profile of the narrow beam component; at leasttwo current drivers, including a first current driver coupled to thefirst IR emitter, and a second current driver coupled to the second IRemitter; and processing circuitry communicative with the current driversto instruct each current driver to deliver a selected amount of power tothe coupled IR emitter. The processing circuitry comprises a processorand a memory having encoded thereon program code executable by theprocessor to perform the aforementioned method for generating aninfrared (IR) beam for illuminating a scene to be imaged. The first andsecond IR emitters can be aligned such that the wide and narrow beamcomponents are directed at the same location in the scene.

The apparatus can further comprise an imager communicative with theprocessing circuitry, a zoom lens having variable focal lengths andbeing optically coupled to the imager, and a lens driver communicativewith the zoom lens and the processing circuitry. The memory can furthercomprise a beam profile-to-focal length map comprising a series of focallength increments of the zoom lens and their corresponding desiredlinear profiles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of components of an imagingapparatus with a zoom adaptive IR beam according to one embodiment ofthe invention.

FIG. 2 is a perspective view of the imaging apparatus embodied as asecurity camera.

FIG. 3 is a flow chart showing steps performed by a program forgenerating an IR beam with a linear profile that varies with focallength of a zoom lens of the security camera.

FIG. 4 is a graph of exemplary linear profiles of a wide angle LED setand a narrow angle LED set of the imaging apparatus at the shortestfocal length of a 3 to 9 mm zoom lens.

FIG. 5 is a graph of exemplary focal length to optimal power output ofthe wide angle LED set of an imaging apparatus having the linearprofiles of the wide and narrow angle LED sets and zoom lens shown inFIG. 4.

DETAILED DESCRIPTION

Embodiments of the invention described herein relate to a variable IRilluminator apparatus and method for generating an IR beam used toilluminate a scene to be imaged, wherein the IR beam has an illuminationpattern with a linear profile that can be varied. In this description,“illumination pattern” refers to the two-dimensional irradiancedistribution of the IR beam in the scene, and “linear profile” refers tothe irradiance distribution of the IR beam along a selected line throughthe centre of the illumination pattern. Typically, an IR beam isradially symmetrical in which case the linear profile will define thecharacteristics of the illumination pattern. Such a variable IR beam canbe used in an imaging apparatus such as a security camera whichcomprises a varifocal (zoom) lens with a variable focal length (zoom).The variable IR illuminator can be part of the imaging apparatus and beused to vary the linear profile of an IR beam on a scene captured by theimaging apparatus. The imaging apparatus includes a processor with amemory having encoded thereon program code executable by the processorto vary the linear profile of the IR beam as the focal length of thezoom lens is varied. The linear profile of the IR beam at a given focallength can be selected to provide improved uniformity and/or improvedirradiance of the IR beam at that focal length, when compared to an IRilluminator that produces an illumination pattern having the same linearprofile for all focal lengths.

Having an IR beam with a linear profile that can vary with the focallength of the zoom lens is beneficial because as a zoom lens zooms in(i.e. the focal length lengthens), the field of view of a captured imageis reduced. To maximize the signal-to-noise ratio of the captured image,as much of the IR illumination beam's power should be directed into thefield of view as evenly as possible at any given focal length. However,an IR beam with a fixed illumination pattern (i.e. a beam with anon-varying linear profile) can only be optimized for the field of viewat one particular focal length; this results in substantial parts of theIR beam being projected outside the field of view at focal lengths thatare longer than the optimized focal length and an IR beam that is unevenwith a bright spot at the centre of the image at focal lengths that areshorter than the optimized focal length. As will be described in detailbelow, in embodiments of the imaging apparatus described herein, thevariable IR illuminator comprises at least two IR emitters which eachproduce an IR beam of different linear profiles, and which can becombined at different power ratios to generate an IR beam of differentlinear profiles; this enables the imaging apparatus to select an IR beamwith a linear profile that is particularly suited to a particular focallength of the zoom lens. A particularly suited linear profile is onewhich meets or is below a target standard deviation and/or meets orexceeds a target irradiance.

Referring now to FIG. 1, an imaging apparatus 10 according to oneembodiment comprises the following major components: a zoom lens 12, animager 14 optically coupled to the zoom lens 12, a lens driver 16mechanically coupled to the zoom lens 12 and operable to change thefocal length of the zoom lens, an IR illuminator 18 comprising a pair ofIR emitters 18(a), 18(b) each producing an IR beam with a differentlinear profile (respectively, “wide angle IR emitter” 18(a) and “narrowangle IR emitter” 18(b)), a current driver 20(a), 20(b) for each IRemitter 18(a), 18(b), and control and processing circuitry 22communicative with the imager 14, lens driver 16, and current drivers20(a), 20(b).

While FIG. 1 shows an embodiment with only a pair of IR emitters 18(a),18(b), other embodiments can features more than two IR emitters eachproducing an IR beam of a different linear profile, and which can becombined to produce an IR beam with a variable linear profile.

Referring to FIG. 2, the imaging apparatus 10 can be embodied as asecurity camera or surveillance camera. The security camera 10 has ahousing 30 which houses the aforementioned major components of theimaging apparatus 10, and a movable mount 32 for mounting the camera 10to a surface such as a ceiling. The zoom lens 12 is mounted at the frontof the camera 10, and a printed circuit board (“PCB”, not shown) is alsomounted at the front of the camera 10 around the zoom lens 12; the wideangle IR emitter 18(a) and narrow angle IR emitter 18(b) arerespectively mounted on this PCB and face the same direction as the zoomlens 12 and serve to illuminate the field of view of the zoom lens withinfrared light. The IR emitters 18(a), 18(b) are aligned such thatillumination pattern produced by each IR emitter 18(a), 18(b) is centredon the same location in the field of view, and more particularly, at thecentre of the field of view of the zoom lens 12. The imaging apparatus10 can be electrically coupled to a power source such as a nearbyelectrical outlet (not shown) and is configured with a maximum powerrating that defines the total available power that can be sent to the IRemitters 18(a), 18(b).

Each IR emitter 18(a), 18(b) in this embodiment comprises a set ofinfrared emitting diodes (IRED) 34. Such IRED sets are known in the art;one suitable such IRED set comprises a pair of Osram SFH4715S IREDs.Each IR emitter 18(a), 18(b) also comprises a lenslet 36 for each IRED34; the lenslet 36 is configured to shape the RED emission into an IRbeam having an illumination pattern with a particular linear profile. Inparticular, the lenslets 36 for the wide angle IR emitter 18(a) willproduce an IR beam with a linear profile that is relatively widelydispersed (hereinafter referred to as the “wide beam component”), andthe lenslets 36 for the narrow angle IR emitter 18(b) will produce an IRbeam with a linear profile that is relatively narrowly dispersed, i.e.(hereinafter referred to as the “narrow beam component”). Such lensletsare known in the art; one suitable such lenslet can be provided byLedil.

The current drivers 20(a), 20(b) are designed to regulate the currentdelivered to the IR emitters 18(a), 18(b). The current drivers 20(a),20(b) can be controlled to deliver all of the total available power toone or the other of the IR emitters 18(a), 18(b), or vary the powerratio between the two emitters 18(a), 18(b). Such current drivers areknown in the art; one suitable such current driver is the AL8805 BuckLED Driver by On Semiconductor. The current drivers 20(a), 20(b) areeach communicatively coupled to a respective general purposeinput/output (GPIO) pin 38(a), 38(b) on a circuit board inside thehousing which contains the processing circuitry 22 (otherwise known asmain system on chip (SoC)) of the surveillance camera 10. The SoC 22includes a processor and a memory (CPU) 40 having encoded thereonprogram code that is executed by the processor to operate the securitycamera 10. This program code includes instructions for sending a controlsignal from each GPIO pin 38(a), (b) to each current driver 20(a), 20(b)to produce the IR beam. As will be described in detail below, theprogram code also includes instructions for combining the wide andnarrow beam components in a manner that produces a combined IR beam witha linear profile that is suitable for a particular focal length of thezoom lens 12.

The processing circuitry 22 also comprises an interface bus with pins42, 44 that are communicatively coupled to the lens driver 16 and imager14. The imager 14 is configured to capture light in the infraredspectrum, and can be for example, a digital sensor such as acomplementary metal-oxide-semiconductor (CMOS) sensor. Thespecifications of the imager 14 and the zoom lens 12 can be selectedbased on an operator's requirements and performance expectations.Operation of zoom lenses and imaging sensors in a surveillance cameraare well known in the art and thus the operation of the imager 14, lensdriver 16 and zoom lens 12 are not described in further detail here.

Referring now to FIG. 3, the program code stored on the memory of theCPU and executable by the processor of the CPU includes instructions forperforming a method for generating an IR beam with a linear profile thatvaries with focal length of the zoom lens (“zoom adaptive IR beam”).More particularly, the program code when executed selects a power ratioof the wide beam component to the narrow beam component to produce an IRbeam with a linear profile that suits a particular focal length of thezoom lens. The program code comprises the following steps:

-   (a) read lens driver 16 to determine current focal length of the    zoom lens;-   (b) read a beam profile-to-focal length map to determine the linear    profile of the IR beam that is associated with the current focal    length; and-   (c) send control signals to each current driver 20(a), 20(b) at the    power ratio associated with the determined linear profile, to    generate an IR beam having the determined linear profile.

The beam profile-to-focal length map is a database comprising the IRbeam linear profile and associated power ratio for each focal lengthincrement of the zoom lens. The IR beam linear profile and associatedpower ratio can be determined for each focal length increment bycarrying out the following steps:

First, the security camera 10 captures two images with the zoom lens 12at the shortest focal length ƒ (step 100). The first image (“img1”) iscaptured using an IR beam with all of the available power sent to thewide angle IR emitter 18(a) and no power sent to the narrow angle IRemitter 18(b) (“W@100%, N@0%”); in other words, the power ratio of thewide beam component to the narrow beam component (“wide/narrow beampower ratio”) of this IR beam is 100:0. The second image (“img2”) iscaptured using an IR beam with a wide/narrow beam power ratio of 0:100(“W@0%, N@100%”). The first image thus corresponds to the wide beamcomponent emitted by the wide angle IR emitter 18(a), and the secondimage corresponds to the narrow beam component emitted by the narrowangle IR emitter 18(b). Then, the linear profiles of the first andsecond images (“LinearProfile(img1)”, “LinearProfile(img2)”) aredetermined by determining the IR irradiance I at each pixel P across thewidth of each image, wherein each image has an image width of n pixels.The linear profiles are stored in a database on the memory (step 102).

Then, a series of steps are carried out that determine a suitablewide/narrow beam power ratio of the IR beam for each focal lengthincrement, starting at the shortest focal length ƒ(“minimumFocalLength”) and advancing in selected increments ƒ′ to thelongest focal length. A suitable wide/narrow beam power ratio is onewhich produces an IR beam having the maximum IR power delivered to thefield of view at focal length ƒ′ and a linear profile that has astandard deviation that is below a target standard deviation. The targetstandard deviation can be empirically derived (step 104), and can beselected to produce an acceptably even distribution of IR intensityacross the image width.

Starting at the shortest focal length fƒ (step 106), the field of viewis determined for each focal length increment ƒ′. As the field of viewdecreases as a function of increasing focal length, the field of viewFOV at a focal length increment ƒ′ can be approximated by the followingequation:

FOV _(ƒ′) =[n(1−f/f′)/2 . . . n(1+f/f′)/2]

Once the field of view at the focal length increment ƒ′ has beendetermined, the linear profile for the narrow beam componentL_(N′1 . . . n]) and wide beam component L_(W′[1 . . . n]) at this focallength is determined (step 108) and stored in the memory.

For each focal length increment ƒ′, the linear profile of the combinedIR beam at different wide/narrow beam power ratios is iterativelydetermined until a power ratio is found which produces an IR beam havinga standard deviation that is smaller than the target standard deviation.This determination is performed in an iterative loop starting with awide/narrow beam power ratio of 0:100 (“powerWide=0%, powerNarrow=0%”)(step 110) and iterating through a selected number of power ratios ofdecreasing increments of the power to the narrow angle emitter. Theincrement intervals can be selected depending on the factors such asdesired processing speed, and can for example be 20% resulting in sixpower ratios 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0. The linearprofile of the combined IR beam at each power ratio is determined bytaking the weighted average L_(c) of the wide and narrow beam linearprofiles L_(w′) and L_(N′) at the selected power ratio (step 112). Then,the standard deviation of the linear profile of the combined IR beam isdetermined (step 114) and compared to the target standard deviation(step 116). If the determined standard deviation is not less that thetarget standard deviation and the selected power ratio is not 100:0, thenext power ratio is selected (by reducing the narrow beam componentpower by 20% and increasing the wide beam component power by 20%) (step118) and the method returns back to step 112 wherein the linear profileof the combined IR beam is calculated again at the next power ratio.

As noted above, the target standard deviation represents an acceptabledistribution of the IR beam across the image width. By starting with awide/narrow beam power ratio of 0:100 at the shortest focal length andreducing the power to the narrow beam component with each increasingincrement of focal length until a power ratio is found with a standarddeviation below the target standard deviation, the combined IR beamshould have the maximum IR power (maximum irradiance) deliverable to thefield of view of the camera for the available power ratio combinations,since that power ratio will provide the maximum possible power to thenarrow beam component.

Steps 112 to 118 are repeated until a power ratio is found whichproduces a linear profile of the combined IR beam with a standarddeviation that is less than the target standard deviation. Once thisoccurs and provided that the power ratio is not 100:0, an optimal powerratio for the combined IR beam is determined (step 120) by linearlyinterpolating for the target standard deviation according to thefollowing equation:

OptimalPowerWide=powerWide−(100/k)×(T _(std)−stddev)/(lastStddev−stddev)

wherein

-   OptimalPowerWide is the optimal power % of the wide beam component;-   powerWide is the power % of the wide beam component at the power    ratio that produces a standard deviation (stdDev) below the target    standard deviation (the power % of the narrow beam component can be    easily calculated as 100%−power % of the wide beam component);-   T_(std) is the target standard deviation; and    -   lastStddev is the standard deviation at the power ratio        immediately preceding the power ratio associated with stdDev.

If the power ratio is 0:100, then the optimal power ratio is deemed tobe 0:100 and the linear interpolation step is not performed (Step 121).

Once the optimal power ratio is determined, this value along with thecorresponding focal length f′ is saved in the map (step 122), and themethod advances to the next focal length increment ƒ′ (step 124) and themethod returns back to step 106 to determine the optimal power ratio ofthe combined IR beam at the next focal length increment ƒ′. Once themethod has advanced through all the focal length increments, the beamprofile-to-focal length map is produced representing the optimal powerratios for the combined IR beam at each focal length increment ƒ′.

In an alternative embodiment, the beam profile-to-focal length map canbe generated empirically by projecting multiple combinations of powerratios for the wide and narrow beam components at each focal length, andmanually selecting the power ratio that produces an IR beam with alinear profile with an acceptable standard deviation and irradiance.

According to another embodiment (not shown), an IR illuminator can beprovided with the same wide and narrow angle IR emitters 18(a), 18(b) asin embodiment shown in FIGS. 1 to 3 to produce an IR beam with avariable linear profile, but this IR illuminator does not form part ofan imaging apparatus. This IR illuminator can, for example, be anexternal IR illuminator that is used in conjunction with an IR securitycamera.

As this IR illuminator is not part of an imaging apparatus, theprocessing circuitry of the IR illuminator does not necessarily need toinclude instructions for varying the IR beam's linear profile with thefocal length of the imaging apparatus' zoom lens. Instead, the IRilluminator can be provided with a user interface which allows anoperator to manually select a desired linear profile for the IR beam.Alternatively or additionally, the IR illuminator can be provided with awireless communications means like Wi-Fi, or a communications port forconnecting an Ethernet or other communications cable to an imagingapparatus, to allow the IR illuminator to communicate with the imagingapparatus. The processing circuitry of the IR illuminator or theconnected imaging apparatus can be programmed with the beamprofile-to-focal length map, as well as with program code which causesthe IR illuminator to generate an IR beam with a linear profile thatvaries with the focal length of the imaging apparatus' zoom lens.

EXAMPLES

Referring now to FIGS. 4 and 5, the linear profiles of the wide andnarrow beam components are shown for a security camera having a 3 to 9mm zoom lens, and image width n of 2015 pixels. The irradiance level ateach pixel n is recorded as a pixel value of the image sensor, which inthis case has 255 different pixel values for each pixel. It can be seenin FIG. 4 that the standard deviation of the narrow beam component issubstantially higher than that of the wide beam component, with aluminous flux peaking in the centre of the image.

FIG. 5 shows a map of wide angle power settings of the IR beam for eachfocal length increment ƒ′. Here it can be seen that over a focal lengthof 3 to 9 mm, that the power % of the wide beam component varies from80% to 20%. This map can be used to determine the wide/narrow beam powerratio for the IR beam at each focal length increment ƒ′.

While the present invention has been described herein by the preferredembodiments, it will be understood to those skilled in the art thatvarious changes may be made and added to the invention. The changes andalternatives are considered within the spirit and scope of the presentinvention. For example, while this disclosure has been directed to IRimaging, the invention can be applied to imaging using other parts ofthe electromagnetic radiation spectrum, such as the visible lightspectrum In particular, a visible light illuminator can be providedwhich is comprised of two or more illuminator components that produce atleast a wide beam component and a narrow beam component that can becombined to produced a combined visible light illumination beam ofvariable linear profile. More particularly, the linear profile of theillumination beam can be varied with focal length increment of a zoomlens of an imaging apparatus.

What is claimed is:
 1. A method for generating an infrared (IR) beam forilluminating a scene to be imaged, the method comprising: (a) providingat least two IR emitters, including a first IR emitter operable to emita wide beam component of the IR beam, and a second IR emitter operableto emit a narrow beam component of the IR beam, wherein the wide beamcomponent has a linear profile that has a lower standard deviation thana linear profile of the narrow beam component; (b) selecting a desiredlinear profile for the IR beam, and selecting a power ratio of powerdirected to the first IR emitter and power directed to the second IRemitter that produces the IR beam with the desired linear profile whenthe narrow beam component and wide beam component are combined; and (c)producing the IR beam by directing power to the first and second IRemitters at the selected power ratio to generate the wide and narrowbeam components, and combining the generated wide and narrow beamcomponents.
 2. A method as claimed in claim 1 wherein the generated wideand narrow beam components are combined by directing the centres of thewide and narrow beam components on the same location in the scene.
 3. Amethod as claimed in claim 2 wherein the desired linear profile of theIR beam has a standard deviation that is less than or equal to a targetstandard deviation.
 4. A method as claimed in claim 3 further comprisingimaging the scene at a selected focal length, wherein the selected focallength has an associated field of view, and the desired linear profilefor the selected focal length has a standard deviation that is less thanor equal to the target standard deviation and a highest availableirradiance within the field of view.
 5. A method as claimed in claim 4wherein the highest available irradiance is the power ratio having thehighest proportion of power directed to second IR emitter and whichproduces an IR beam with a standard deviation less than or equal to thetarget standard deviation.
 6. A method as claimed in claim 5 furthercomprising imaging the scene at different focal lengths each having arespective different field of view, and producing an IR beam with adesired linear profile corresponding to each different focal length,wherein each desired linear profile has a standard deviation that isless than or equal to the target standard deviation and the highestavailable irradiance for the field of view associated with thecorresponding focal length.
 7. A method as claimed in claim 6 whereinthe imaging is performed by an imaging apparatus having a zoom lens withvariable focal lengths, and the method comprises determining a currentfocal length of the zoom lens, selecting the desired linear profilecorresponding to the current focal length, producing an IR beam at thedesired focal length, and imaging a scene illuminated by the IR beam atthe current focal length.
 8. A method as claimed in claim 7 whereinselecting the desired linear profile corresponding to the current focallength comprising accessing a beam profile-to-focal length mapcomprising a series of focal length increments and their correspondingdesired linear profiles, and selecting the linear profile in the mapwith a corresponding focal length increment equal to the current focallength.
 9. An apparatus for illuminating a scene to be imaged withinfrared radiation, comprising: (a) at least two IR emitters, includinga first IR emitter operable to emit a wide beam component of the IRbeam, and a second IR emitter operable to emit a narrow beam componentof the IR beam, wherein the wide beam component has a linear profilethat has a lower standard deviation than a linear profile of the narrowbeam component; (b) at least two current drivers, including a firstcurrent driver coupled to the first IR emitter, and a second currentdriver coupled to the second IR emitter; and (c) processing circuitrycommunicative with the current drivers to instruct each current driverto deliver a selected amount of power to the coupled IR emitter, andcomprising a processor and a memory having encoded thereon program codeexecutable by the processor to perform a method as claimed in claim 1.10. An apparatus as claimed in claim 9 wherein the first and second IRemitters are aligned such that the wide and narrow beam components aredirected at the same location in the scene.
 11. An apparatus as claimedin claim 10 further comprising an imager communicative with theprocessing circuitry, a zoom lens having variable focal lengths andbeing optically coupled to the imager, and a lens driver communicativewith the zoom lens and the processing circuitry.
 12. An apparatus asclaimed in claim 11 wherein the memory further comprises a beamprofile-to-focal length map comprising a series of focal lengthincrements of the zoom lens and their corresponding desired linearprofiles.